Dr. Christopher Ryan is the writer of Sex at Dawn, a definitive book on human sexuality in the modern age, but also way back in our past. Is monogamy natural, or does promiscuity come easier to us? Where did our modern ways of sex, grouping, child-rearing, and social structuring come from, and how did ancient humans mitigate the same topics? How have penises and vaginas evolved over time? Christopher Ryan discusses our prehistoric sexual history and how we've evolved and changed into the modern era.

Christopher Ryan is also a regular contributor to Psychology Today and runs the podcast, Tangentially Speaking with Dr. Christopher Ryan. Before writing Sex at Dawn with his wife, Ryan travelled the world teaching English to prostitutes in Bangkok and self-defense (Kung Fu) to land-reform activists in Mexico.